Android 事件分发
本篇文章主要简单介绍下Android中的事件分发,和大家一起学习,进步,有问题也希望大家及时指证修改.
1: onClick和OnTouch
首先我们在单独的activity中添加个按钮button.增加点击事件setOnClickListener:
button.setOnClickListener(v -> Log.i(TAG, "onClick: "));
接着添加OnTouch:
button.setOnTouchListener((v, event) -> {
Log.i(TAG, "onTouch: " + event.getAction());
return false;
});
我们执行下点击事件.可以看到输出如下:
2024-04-09 20:54:11.219 17770-17770/? I/testxxx: onTouch: 0
2024-04-09 20:54:11.234 17770-17770/? I/testxxx: onTouch: 2
2024-04-09 20:54:11.294 17770-17770/? I/testxxx: onTouch: 2
2024-04-09 20:54:11.299 17770-17770/? I/testxxx: onTouch: 2
2024-04-09 20:54:11.300 17770-17770/? I/testxxx: onTouch: 1
2024-04-09 20:54:11.306 17770-17770/? I/testxxx: onClick:
OnTouch的事件比较多一些,包含了按下,移动,抬起事件.
事件执行的顺序我们可以看到是OnTouch->onClick.
我们在修改下OnTouch方法:
2024-04-10 10:03:53.245 19437-19437/? I/testxxx: onTouch: 0
2024-04-10 10:03:53.264 19437-19437/? I/testxxx: onTouch: 2
2024-04-10 10:03:53.298 19437-19437/? I/testxxx: onTouch: 2
2024-04-10 10:03:53.304 19437-19437/? I/testxxx: onTouch: 2
2024-04-10 10:03:53.305 19437-19437/? I/testxxx: onTouch: 1
可以看到这里已经没有onCLick事件的执行了.
原因是:onTouch返回true,就代表了该点击事件被onTouch消费掉了,不会继续向下执行. 具体的源码分析可以继续往下看.
2: onInterceptTouchEvent/dispatchTouchEvent/onTouchEvent
首先我们自定义下relationlayout以及button:
package com.test.touchtest;
import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.widget.RelativeLayout;
/**
* @Author: zh
* @Time: 24-4-10.
* @Describe:
*/
public class CustomLayout extends RelativeLayout {
private static final String TAG = "CustomLayout";
public CustomLayout(Context context) {
super(context);
}
public CustomLayout(Context context, AttributeSet attrs) {
super(context, attrs);
}
public CustomLayout(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
Log.i(TAG, "onInterceptTouchEvent: " + ev.getAction());
return super.onInterceptTouchEvent(ev);
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
Log.i(TAG, "dispatchTouchEvent: " + ev.getAction());
return super.dispatchTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.i(TAG, "onTouchEvent: " + event.getAction());
return super.onTouchEvent(event);
}
}
package com.test.touchtest;
import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
/**
* @Author: zh
* @Time: 24-4-10.
* @Describe:
*/
public class CustomButton extends androidx.appcompat.widget.AppCompatButton {
private static final String TAG = "CustomButton";
public CustomButton(Context context) {
super(context);
}
public CustomButton(Context context, AttributeSet attrs) {
super(context, attrs);
}
public CustomButton(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
Log.i(TAG, "dispatchTouchEvent: " + ev.getAction());
return super.dispatchTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
Log.i(TAG, "onTouchEvent: " + event.getAction());
return super.onTouchEvent(event);
}
}
执行下button的点击.
2024-04-10 10:16:57.059 25026-25026/com.test.touchtest I/CustomLayout: dispatchTouchEvent: 0
2024-04-10 10:16:57.059 25026-25026/com.test.touchtest I/CustomLayout: onInterceptTouchEvent: 0
2024-04-10 10:16:57.060 25026-25026/com.test.touchtest I/CustomButton: dispatchTouchEvent: 0
2024-04-10 10:16:57.060 25026-25026/com.test.touchtest I/CustomButton: onTouchEvent: 0
2024-04-10 10:16:57.077 25026-25026/com.test.touchtest I/CustomLayout: dispatchTouchEvent: 2
2024-04-10 10:16:57.077 25026-25026/com.test.touchtest I/CustomLayout: onInterceptTouchEvent: 2
2024-04-10 10:16:57.077 25026-25026/com.test.touchtest I/CustomButton: dispatchTouchEvent: 2
2024-04-10 10:16:57.077 25026-25026/com.test.touchtest I/CustomButton: onTouchEvent: 2
2024-04-10 10:16:57.116 25026-25026/com.test.touchtest I/CustomLayout: dispatchTouchEvent: 1
2024-04-10 10:16:57.116 25026-25026/com.test.touchtest I/CustomLayout: onInterceptTouchEvent: 1
2024-04-10 10:16:57.117 25026-25026/com.test.touchtest I/CustomButton: dispatchTouchEvent: 1
2024-04-10 10:16:57.117 25026-25026/com.test.touchtest I/CustomButton: onTouchEvent: 1
2024-04-10 10:16:57.126 25026-25026/com.test.touchtest I/custom: onClick:
可以看到大概的执行顺序如下:
- ViewGroup: dispatchTouchEvent
- ViewGroup: onInterceptTouchEvent
- Button: dispatchTouchEvent
- Button: onTouchEvent
- Button: onClick
我们在增加下button的setOnToucnListener,打印输出如下:
2024-04-10 11:01:38.824 2160-2160/? I/CustomLayout: dispatchTouchEvent: 0
2024-04-10 11:01:38.825 2160-2160/? I/CustomLayout: onInterceptTouchEvent: 0
2024-04-10 11:01:38.825 2160-2160/? I/CustomButton: dispatchTouchEvent: 0
2024-04-10 11:01:38.826 2160-2160/? I/customActivity: onTouch: 0
2024-04-10 11:01:38.826 2160-2160/? I/CustomButton: onTouchEvent: 0
2024-04-10 11:01:38.843 2160-2160/? I/CustomLayout: dispatchTouchEvent: 2
2024-04-10 11:01:38.843 2160-2160/? I/CustomLayout: onInterceptTouchEvent: 2
2024-04-10 11:01:38.843 2160-2160/? I/CustomButton: dispatchTouchEvent: 2
2024-04-10 11:01:38.843 2160-2160/? I/customActivity: onTouch: 2
2024-04-10 11:01:38.843 2160-2160/? I/CustomButton: onTouchEvent: 2
2024-04-10 11:01:38.902 2160-2160/? I/CustomLayout: dispatchTouchEvent: 1
2024-04-10 11:01:38.902 2160-2160/? I/CustomLayout: onInterceptTouchEvent: 1
2024-04-10 11:01:38.902 2160-2160/? I/CustomButton: dispatchTouchEvent: 1
2024-04-10 11:01:38.902 2160-2160/? I/customActivity: onTouch: 1
2024-04-10 11:01:38.902 2160-2160/? I/CustomButton: onTouchEvent: 1
2024-04-10 11:01:38.908 2160-2160/? I/customActivity: onClick:
可以看到大概的执行顺序如下:
- ViewGroup: dispatchTouchEvent
- ViewGroup: onInterceptTouchEvent
- Button: dispatchTouchEvent
- Button: onTouch
- Button: onTouchEvent
- Button: onClick
3: 源码分析
我们简单看下源码:
-
View的onTouchEvent:
public boolean onTouchEvent(MotionEvent event) { final float x = event.getX(); final float y = event.getY(); final int viewFlags = mViewFlags; final int action = event.getAction(); final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE; if ((viewFlags & ENABLED_MASK) == DISABLED) { if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) { setPressed(false); } mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN; // A disabled view that is clickable still consumes the touch // events, it just doesn't respond to them. return clickable; } if (mTouchDelegate != null) { if (mTouchDelegate.onTouchEvent(event)) { return true; } } if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) { switch (action) { case MotionEvent.ACTION_UP: mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN; if ((viewFlags & TOOLTIP) == TOOLTIP) { handleTooltipUp(); } if (!clickable) { removeTapCallback(); removeLongPressCallback(); mInContextButtonPress = false; mHasPerformedLongPress = false; mIgnoreNextUpEvent = false; break; } boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0; if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) { // take focus if we don't have it already and we should in // touch mode. boolean focusTaken = false; if (isFocusable() && isFocusableInTouchMode() && !isFocused()) { focusTaken = requestFocus(); } if (prepressed) { // The button is being released before we actually // showed it as pressed. Make it show the pressed // state now (before scheduling the click) to ensure // the user sees it. setPressed(true, x, y); } if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) { // This is a tap, so remove the longpress check removeLongPressCallback(); // Only perform take click actions if we were in the pressed state if (!focusTaken) { // Use a Runnable and post this rather than calling // performClick directly. This lets other visual state // of the view update before click actions start. if (mPerformClick == null) { mPerformClick = new PerformClick(); } if (!post(mPerformClick)) { performClickInternal(); } } } if (mUnsetPressedState == null) { mUnsetPressedState = new UnsetPressedState(); } if (prepressed) { postDelayed(mUnsetPressedState, ViewConfiguration.getPressedStateDuration()); } else if (!post(mUnsetPressedState)) { // If the post failed, unpress right now mUnsetPressedState.run(); } removeTapCallback(); } mIgnoreNextUpEvent = false; break; case MotionEvent.ACTION_DOWN: if (event.getSource() == InputDevice.SOURCE_TOUCHSCREEN) { mPrivateFlags3 |= PFLAG3_FINGER_DOWN; } mHasPerformedLongPress = false; if (!clickable) { checkForLongClick(0, x, y); break; } if (performButtonActionOnTouchDown(event)) { break; } // Walk up the hierarchy to determine if we're inside a scrolling container. boolean isInScrollingContainer = isInScrollingContainer(); // For views inside a scrolling container, delay the pressed feedback for // a short period in case this is a scroll. if (isInScrollingContainer) { mPrivateFlags |= PFLAG_PREPRESSED; if (mPendingCheckForTap == null) { mPendingCheckForTap = new CheckForTap(); } mPendingCheckForTap.x = event.getX(); mPendingCheckForTap.y = event.getY(); postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout()); } else { // Not inside a scrolling container, so show the feedback right away setPressed(true, x, y); checkForLongClick(0, x, y); } break; case MotionEvent.ACTION_CANCEL: if (clickable) { setPressed(false); } removeTapCallback(); removeLongPressCallback(); mInContextButtonPress = false; mHasPerformedLongPress = false; mIgnoreNextUpEvent = false; mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN; break; case MotionEvent.ACTION_MOVE: if (clickable) { drawableHotspotChanged(x, y); } // Be lenient about moving outside of buttons if (!pointInView(x, y, mTouchSlop)) { // Outside button // Remove any future long press/tap checks removeTapCallback(); removeLongPressCallback(); if ((mPrivateFlags & PFLAG_PRESSED) != 0) { setPressed(false); } mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN; } break; } return true; } return false; }我们关注下MotionEvent.ACTION_UP事件,可以看到在事件处理的最后有这么一段代码:
if (mPerformClick == null) { mPerformClick = new PerformClick(); } if (!post(mPerformClick)) { performClickInternal(); } -
performClickInternal() 源码如下:
private boolean performClickInternal() { // Must notify autofill manager before performing the click actions to avoid scenarios where // the app has a click listener that changes the state of views the autofill service might // be interested on. notifyAutofillManagerOnClick(); return performClick(); } -
performClick()源码:
public boolean performClick() { // We still need to call this method to handle the cases where performClick() was called // externally, instead of through performClickInternal() notifyAutofillManagerOnClick(); final boolean result; final ListenerInfo li = mListenerInfo; if (li != null && li.mOnClickListener != null) { playSoundEffect(SoundEffectConstants.CLICK); li.mOnClickListener.onClick(this); result = true; } else { result = false; } sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED); notifyEnterOrExitForAutoFillIfNeeded(true); return result; }可以看到在li != null && li.mOnClickListener != null条件下,执行了:
li.mOnClickListener.onClick(this);
所以也可以解释了:
事件onTouchEvent()->onClick()的执行顺序.
然后我们看下View的dispathTouchEvent()的源码:
public boolean dispatchTouchEvent(MotionEvent event) {
// If the event should be handled by accessibility focus first.
if (event.isTargetAccessibilityFocus()) {
// We don't have focus or no virtual descendant has it, do not handle the event.
if (!isAccessibilityFocusedViewOrHost()) {
return false;
}
// We have focus and got the event, then use normal event dispatch.
event.setTargetAccessibilityFocus(false);
}
boolean result = false;
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(event, 0);
}
final int actionMasked = event.getActionMasked();
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Defensive cleanup for new gesture
stopNestedScroll();
}
if (onFilterTouchEventForSecurity(event)) {
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
if (!result && onTouchEvent(event)) {
result = true;
}
}
if (!result && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
}
// Clean up after nested scrolls if this is the end of a gesture;
// also cancel it if we tried an ACTION_DOWN but we didn't want the rest
// of the gesture.
if (actionMasked == MotionEvent.ACTION_UP ||
actionMasked == MotionEvent.ACTION_CANCEL ||
(actionMasked == MotionEvent.ACTION_DOWN && !result)) {
stopNestedScroll();
}
return result;
}
可以看到源码中的这段代码:
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
if (!result && onTouchEvent(event)) {
result = true;
}
这里调用了mOnTouchListener.onTouch事件.
所以也就证明了之前事件执行的顺序:
view的dispatchTouchEvent()->mOnTouchListener.onTouch()->onTouchEent()->onClick().
并且如果li.mOnTouchListener.onTouch(this, event)返回true,也可以看到onTouchEvent(event)并不会执行.
也就解释了我们前面如果修改了onTouch返回值为true,并不会执行onClick事件的原因.
接着我们在看下ViewGroup的dispatchTouchEvent()源码:
public boolean dispatchTouchEvent(MotionEvent ev) {
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
}
// If the event targets the accessibility focused view and this is it, start
// normal event dispatch. Maybe a descendant is what will handle the click.
if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) {
ev.setTargetAccessibilityFocus(false);
}
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// Handle an initial down.
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Throw away all previous state when starting a new touch gesture.
// The framework may have dropped the up or cancel event for the previous gesture
// due to an app switch, ANR, or some other state change.
cancelAndClearTouchTargets(ev);
resetTouchState();
}
// Check for interception.
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev);
ev.setAction(action); // restore action in case it was changed
} else {
intercepted = false;
}
} else {
// There are no touch targets and this action is not an initial down
// so this view group continues to intercept touches.
intercepted = true;
}
// If intercepted, start normal event dispatch. Also if there is already
// a view that is handling the gesture, do normal event dispatch.
if (intercepted || mFirstTouchTarget != null) {
ev.setTargetAccessibilityFocus(false);
}
// Check for cancelation.
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
// Update list of touch targets for pointer down, if needed.
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
if (!canceled && !intercepted) {
// If the event is targeting accessibility focus we give it to the
// view that has accessibility focus and if it does not handle it
// we clear the flag and dispatch the event to all children as usual.
// We are looking up the accessibility focused host to avoid keeping
// state since these events are very rare.
View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus()
? findChildWithAccessibilityFocus() : null;
if (actionMasked == MotionEvent.ACTION_DOWN
|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
final int actionIndex = ev.getActionIndex(); // always 0 for down
final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
: TouchTarget.ALL_POINTER_IDS;
// Clean up earlier touch targets for this pointer id in case they
// have become out of sync.
removePointersFromTouchTargets(idBitsToAssign);
final int childrenCount = mChildrenCount;
if (newTouchTarget == null && childrenCount != 0) {
final float x = ev.getX(actionIndex);
final float y = ev.getY(actionIndex);
// Find a child that can receive the event.
// Scan children from front to back.
final ArrayList<View> preorderedList = buildTouchDispatchChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = getAndVerifyPreorderedIndex(
childrenCount, i, customOrder);
final View child = getAndVerifyPreorderedView(
preorderedList, children, childIndex);
// If there is a view that has accessibility focus we want it
// to get the event first and if not handled we will perform a
// normal dispatch. We may do a double iteration but this is
// safer given the timeframe.
if (childWithAccessibilityFocus != null) {
if (childWithAccessibilityFocus != child) {
continue;
}
childWithAccessibilityFocus = null;
i = childrenCount - 1;
}
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
newTouchTarget = getTouchTarget(child);
if (newTouchTarget != null) {
// Child is already receiving touch within its bounds.
// Give it the new pointer in addition to the ones it is handling.
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
resetCancelNextUpFlag(child);
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
// Child wants to receive touch within its bounds.
mLastTouchDownTime = ev.getDownTime();
if (preorderedList != null) {
// childIndex points into presorted list, find original index
for (int j = 0; j < childrenCount; j++) {
if (children[childIndex] == mChildren[j]) {
mLastTouchDownIndex = j;
break;
}
}
} else {
mLastTouchDownIndex = childIndex;
}
mLastTouchDownX = ev.getX();
mLastTouchDownY = ev.getY();
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}
// The accessibility focus didn't handle the event, so clear
// the flag and do a normal dispatch to all children.
ev.setTargetAccessibilityFocus(false);
}
if (preorderedList != null) preorderedList.clear();
}
if (newTouchTarget == null && mFirstTouchTarget != null) {
// Did not find a child to receive the event.
// Assign the pointer to the least recently added target.
newTouchTarget = mFirstTouchTarget;
while (newTouchTarget.next != null) {
newTouchTarget = newTouchTarget.next;
}
newTouchTarget.pointerIdBits |= idBitsToAssign;
}
}
}
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
// Dispatch to touch targets, excluding the new touch target if we already
// dispatched to it. Cancel touch targets if necessary.
TouchTarget predecessor = null;
TouchTarget target = mFirstTouchTarget;
while (target != null) {
final TouchTarget next = target.next;
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
if (dispatchTransformedTouchEvent(ev, cancelChild,
target.child, target.pointerIdBits)) {
handled = true;
}
if (cancelChild) {
if (predecessor == null) {
mFirstTouchTarget = next;
} else {
predecessor.next = next;
}
target.recycle();
target = next;
continue;
}
}
predecessor = target;
target = next;
}
}
// Update list of touch targets for pointer up or cancel, if needed.
if (canceled
|| actionMasked == MotionEvent.ACTION_UP
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
resetTouchState();
} else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
final int actionIndex = ev.getActionIndex();
final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
removePointersFromTouchTargets(idBitsToRemove);
}
}
if (!handled && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
}
return handled;
}
-
actionMasked == MotionEvent.ACTION_DOWN 条件触发时,将mFirstTouchTarget置为null.
-
disallowIntercept定义了是否禁用事件拦截.可以通过requestDisallowInterceptTouchEvent修改.默认情况下为false.
-
接着进入if条件,默认情况下,执行onInterceptTouchEvent.
public boolean onInterceptTouchEvent(MotionEvent ev) { if (ev.isFromSource(InputDevice.SOURCE_MOUSE) && ev.getAction() == MotionEvent.ACTION_DOWN && ev.isButtonPressed(MotionEvent.BUTTON_PRIMARY) && isOnScrollbarThumb(ev.getX(), ev.getY())) { return true; } return false; } -
在顺序执行可以看到dispatchTransformedTouchEvent()
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel, View child, int desiredPointerIdBits) { final boolean handled; // Canceling motions is a special case. We don't need to perform any transformations // or filtering. The important part is the action, not the contents. final int oldAction = event.getAction(); if (cancel || oldAction == MotionEvent.ACTION_CANCEL) { event.setAction(MotionEvent.ACTION_CANCEL); if (child == null) { handled = super.dispatchTouchEvent(event); } else { handled = child.dispatchTouchEvent(event); } event.setAction(oldAction); return handled; } // Calculate the number of pointers to deliver. final int oldPointerIdBits = event.getPointerIdBits(); final int newPointerIdBits = oldPointerIdBits & desiredPointerIdBits; // If for some reason we ended up in an inconsistent state where it looks like we // might produce a motion event with no pointers in it, then drop the event. if (newPointerIdBits == 0) { return false; } // If the number of pointers is the same and we don't need to perform any fancy // irreversible transformations, then we can reuse the motion event for this // dispatch as long as we are careful to revert any changes we make. // Otherwise we need to make a copy. final MotionEvent transformedEvent; if (newPointerIdBits == oldPointerIdBits) { if (child == null || child.hasIdentityMatrix()) { if (child == null) { handled = super.dispatchTouchEvent(event); } else { final float offsetX = mScrollX - child.mLeft; final float offsetY = mScrollY - child.mTop; event.offsetLocation(offsetX, offsetY); handled = child.dispatchTouchEvent(event); event.offsetLocation(-offsetX, -offsetY); } return handled; } transformedEvent = MotionEvent.obtain(event); } else { transformedEvent = event.split(newPointerIdBits); } // Perform any necessary transformations and dispatch. if (child == null) { handled = super.dispatchTouchEvent(transformedEvent); } else { final float offsetX = mScrollX - child.mLeft; final float offsetY = mScrollY - child.mTop; transformedEvent.offsetLocation(offsetX, offsetY); if (! child.hasIdentityMatrix()) { transformedEvent.transform(child.getInverseMatrix()); } handled = child.dispatchTouchEvent(transformedEvent); } // Done. transformedEvent.recycle(); return handled; }可以看到主要会执行child.dispatchTouchEvent()方法.
这里其实也就验证了我们先前的调用顺序.
ViewGroup的dispatchTouchEvent->ViewGroup的onInterceptTouchEvent->子view的dispatchTouchEvent.